Among conventional equipments of this kind is a trap described in U.S. Pat. No. 4,276,071. This trap, consisting of ceramic filter materials, has a honeycomb construction. A multiple of passages are provided along the longitudinal direction of the trap, and the ends of the passages are closed and opened alternately in both ends of the trap. Exhaust gas introduced to an inlet passage is made to be filtered through narrow gaps of a porous ceramic layer, which constitutes a wall adjacent to another passage. After a multiple of such filtering, the exhaust gas is made to flow out from the outlet side.
A similar equipment is also described in U.S. Pat. No. 4,264,346. The equipment is characterized by the fine structure of the porous ceramic material, which contains ceramic fibers within the foams.
The inventors have examined the conventional traps mentioned above, and noticed that the pressure loss of the exhaust gas passing through the walls of the traps is relatively high and the efficiency of particulate trapping is relatively small.
Further, in the conventional traps, an electric heater is installed on the inlet side of the trap to burn out the carbon particulates. However, carbon particulates in exhaust gas are mainly trapped during their passage through said partition walls which separate said multiple inlet passages from the outlet passages. The location where the largest amount of carbon particulates are trapped is not the inlet side of the filter but a place within the filter and at a distance apart from the inlet end. Although it may be thought to install this heater on the inlet side of the filter, the heat generated in the heater is readily lost by radiation loss. Therefore, ignition of carbon particulates is difficult at the inlet side of the filter.
The inventors have also recognized that the conventional method for manufacturing the honeycomb filter mentioned above is very complicated. Namely, the conventional method comprises the steps of extruding a mixture of ceramics powders and resin to form a rod-like green compact having a multiple of through holes provided along the longitudinal direction thereof, cutting the rod-like compact, closing each one of the both ends of the through holes alternately and sintering the resulting compact. Especially, the step of closing the through holes alternately is very difficult.